In geology, petrifaction or petrification is the original material and the filling of the original pore spaces with minerals. Petrified wood typifies this process, but all organisms, from bacteria to vertebrates, can become petrified. Petrification (petros means stone) occurs when the organic matter is completely replaced by minerals and the fossil is turned to stone. This generally occurs by filling the pores of the tissue, and inter and intra cellular spaces with minerals, then dissolving the organic matter and replacing it with minerals. Researchers at UCLA and the University of Wisconsin–Madison have confirmed that microscopic fossils discovered in a nearly 3.5 billion-year-old piece of rock in Western Australia are the oldest fossils ever found and indeed the earliest direct evidence of life on Earth. The study, published Dec.
Methyl groups most often added to guanine-cytosine base pairs because they are held by three hydrogen bonds, and this decreases the probability of gene expression.
